Synthesis of titanocenes

ABSTRACT

A method for the preparation of titanium-containing metallocene compounds, including constrained geometry titanium complexes, useful as olefin polymerization catalysts is disclosed. Pursuant to the invention, titanium tetrachloride is converted to titanium trichloride by reaction with a metal compound in a non-interfering solvent to produce a mixture useful directly for reaction with a deprotonated metallocene ligand. The titanocene compounds produced pursuant to the invention are free of trace amounts of aluminum which can adversely affect the polymerization reaction.

FIELD OF THE INVENTION

This invention relates to the synthesis of titanocenes includingconstrained geometry titanocene catalysts utilizing a unique titaniumtrichloride reagent.

BACKGROUND OF THE INVENTION

The evolution of metallocene-based catalysts for the polymerization ofethylene and higher α-olefins is reviewed in H. H. Brintzinger, et al.,Angew. Chem. Int. Ed. Engl. 34: 1143-1170 (1995) and in P. C. Mohring,et al., J. Organometal. Chem. 479: 1-29 (1994). The applications ofchiral metallocenes in organic synthesis are reviewed in R. L.Halterman, Chem. Rev. 92: 965-994 (1992). These reviews highlight theapplications of state-of-the art metallocenes. Most often, theseapplications center on the use of titanium containing and other Group IVmetallocenes.

The early preparations of Group IV metallocenes involved reactions ofthe metal tetrahalides, typically the tetrachlorides, with deprotonatedligands, such as sodium cyclopentadienide, to give the metallocenes ingood yields. The metallocenes of current interest possess morecomplicated ligand structures, and their preparations are not asstraightforward. For the preparation of these metallocenes, the use oftitanium tetrachloride often results in low yields of the desiredmetallocenes. Titanium trichloride (TiCl₃) is often specified for use inplace of titanium tetrachloride (TiCl₄); subsequent oxidation gives thedesired metallocenes in greatly improved yields.

For some recent examples which specify the use of titanium trichloride,see L. A. Paquette, et al., Organometallics 14: 4865-4878 (1995); F.Zaegel, et al., Organometallics 14: 4576-4584 (1995); and M. E.Huttenloch, et al., Organometallics 11: 3600-3607 (1992). Halterman,supra, cites references which show the use of titanium trichloride inseveral metallocene preparations. The titanium trichloride so used isproduced from commercial titanium tetrachloride. Titanium trichlorideproduced by hydrogen reduction of the tetrachloride is most often usedin lab-scale preparations. For commercial-scale preparations, this isimpractical due to cost and the presence of acidic impurities. Theseimpurities require purification of the titanium trichloride, typicallyby preparation and isolation of an ether complex, usually thetetrahydrofuran complex.

Commercially-available titanium trichloride is produced by the reductionof the tetrachloride with alkyl aluminum compounds. The titaniumtrichloride so produced contains aluminum chloride, which is notremoved. Typical analyses specify 76-79 weight percent of titaniumtrichloride with the remaining weight percent comprised mostly ofaluminum chloride. The use of aluminum-reduced titanium trichloride inmetallocene preparations often gives products which contain varyingamounts of aluminum-containing impurities. Separation of theseimpurities from the product titanocenes is not straightforward in mostcases, especially on a commercial scale. The presence of theseimpurities can have significant adverse effects during subsequent usesof the titanocenes, particularly in olefin polymerizations.

Accordingly, a need exists for a titanium trichloride reagent useful toproduce titanocenes free of aluminum containing impurities.

DEFINITIONS

For the purposes of this invention, the following terms have the meaningstated:

Titanocene Compound—A compound comprised of titanium bonded to one ormore cyclopentadienyl rings.

Titanocene Ligand—A chemical precursor which contains cyclopentadienylor substituted cyclopentadienyl moieties (including indenyl, fluorenyl,etc.) used to prepare a titanocene compound.

Constrained Geometry Catalyst (CGC)—A catalyst in which the metal centeris contained in a ring structure and covalently bonded to a cyclic groupvia a delocalized π-system and covalently bonded via a sigma-bond toanother atom such as carbon, nitrogen, oxygen, etc. A small ring sizeinduces constraint about the metal atom center. For titanium-containingCGC's, the incorporated titanium atom can be in a formal +4, +3, or +2oxidation state. See EP application 90309496.9, WO 95/00526 and U.S.Pat. No. 5,470,996.

CpSA Ligand—(t-butylamino)(tetramethylcyclopentadienyl)dimethylsilane.

(CpSA)²⁻—doubly-deprotonated CpSA ligand.

(CpSA)²⁻TiCl₂—[(t-butylamido)(tetramethylcyclopentadienyl)dimethylsilane]titanium dichloride.

Substantially Stoichiometric Amount—An amount not less than 90% nor morethat 110% of stoichiometric.

SUMMARY OF THE INVENTION

This invention includes a general method for producing titaniumtrichloride containing mixtures suitable for the preparation oftitanium-containing metallocenes including constrained geometry Ti(IV),Ti(III) and Ti(II) complexes free of aluminum containing impurities.

The titanium trichloride containing mixtures are produced by thepreferably stoichiometric (1:1) reaction of an organometallic compound,such as n-butyl lithium or n-butyl magnesium chloride, with titaniumtetrachloride in a non-interfering solvent medium. These mixtures areused directly without isolation of the titanium trichloride in reactionswith appropriate ligands to produce the desired titanocenes, includingconstrained geometry titanium complexes, in good yields. The resultingtitanocene products are specifically free of aluminum-containingimpurities.

DETAILED DESCRIPTION OF THE INVENTION

The invention is a method for producing a titanium-containingmetallocene compound which comprises separately providing a firstreaction mixture containing titanium trichloride and a second reactionmixture containing a magnesium or alkali metal or alkaline earth metalsalt of a metallocene compound ligand. The first and second mixtures arecombined for reaction to produce an intermediate from which analuminum-free titanocene useful as an olefin polymerization catalyst maybe synthesized.

The first reaction mixture is produced by reacting TiCl₄ with an alkalimetal compound having the formula R_(X)—M or a Grignard reagent havingthe formula RMgX. In each formula, R is a straight or branched chainaliphatic hydrocarbon group, preferably an alkyl group, having 2 to 10carbon atoms. R may also be an alkaline earth metal such as calcium,barium or strontium. X is the value of M. In the formula R_(X)—M, M isan alkali metal such as sodium, potassium or lithium. In the formulaRMgX, X is a halogen, preferably chlorine. n-butyl lithium or n-butylmagnesium chloride are preferred. The reactants are combined insubstantially stoichiometric amounts in a non-interfering, preferablyhydrocarbon, medium.

Useful hydrocarbon media include aliphatic or aromatic hydrocarbons,such as hexane, heptane, cyclohexane, benzene, toluene and xylene.Toluene is preferred for the specific examples shown here. Useful etherand polyether solvents include tetrahydrofuran, diethyl ether, ethyleneglycol dimethyl ether, and dioxane. Mixtures of any hydrocarbon andether solvents are useful for the reaction.

The reaction is preferably accomplished under dry, oxygen-freeconditions. The temperature at which the reaction is convenientlyconducted is −20° C. or 120° C., with the optimum temperature rangebeing 30-40° C.

The second reaction mixture is separately provided by deprotonating thedesired metallocene ligand with the appropriate base by known methods.See, generally, Paquette, et al., supra; Zaegel, et al., supra; andHalterman, supra.

The first reaction mixture, which includes the medium or solvent,titanium trichloride and a metal halide such a LiCl or MCl₂, is addeddirectly without isolation of the titanium trichloride to the seconddeprotonated ligand reaction mixture to produce a first titanocene.

DESCRIPTION OF THE FIGURE

FIG. 1 is a generalized depiction of steps (1), (2), and (3) ascomprised by one embodiment of the invention for preparation of a Ti(IV)complex constrained geometry catalyst.

STEP (1)—ALUMINUM-FREE TICL₃

Step (1) of FIG. 1 illustrates the reaction of TiCl₄ in substantiallystoichiometric amount with n-butyl lithium or n-butyl magnesium chlorideto produce TiCl₃ and lithium or magnesium chloride in a hydrocarbon orether medium, or mixed hydrocarbon and ether medium.

Step (2)—Deprotonation Of a Metallocene Compound Ligand

Step (2) of FIG. 1 illustrates the double deprotonation of themetallocene compound ligand (t-butylamino)(tetramethylcyclopentadienyl)dimethylsilane (CpSA ligand) with anorganometallic deprotonating agent, preferably an organolithium or anorganomagnesium compound (Grignard reagent), in a hydrocarbon medium,preferably toluene.

The solvent medium and the organometallic compound may be the same as ordifferent from the solvent medium and the organometallic compound usedin Step (1). The concentration of the CpSA ligand in the solvent isappropriately 0.05 to 1.5 M, preferably 0.45 to 0.6 M.

Any Grignard reagent may be used to deprotonate the metallocene compoundligand, e.g., CpSA. Useful Grignard reagents have the formula RMgX asdefined above. Isopropyl magnesium chloride is preferred. A practicalrange of Grignard concentration in the solvent is 0.5 to 3.0 M,preferably 1.9 to 2.3 M. For CpSA, the temperature is controlled to be45-50° C. at the end of the Grignard feed, and then heated to 85-90° C.for the prescribed time.

The Step (2) reaction mixture is preferably used directly in Step (3) asthe toluene solution present in the reaction vessel in which it isproduced.

Step (3)—Reaction of TiCl₃ With Deprotonated Ligands—Production of(CpSA)²—TiCl₂

Step (3) of FIG. 1 illustrates one method for reacting the titaniumtrichloride containing reaction mixture of Step (1) with the(CpSA)²⁻containing second reaction mixture of Step (2) to produce[(t-butylamido) (tetramethylcyclopentadienyl) dimethylsilane]titaniumdichloride, (CpSA)²⁻TiCl₂.

In this embodiment of the invention, the agitated Step (1) reactionmixture is transferred directly into the reactor containing agitatedStep (2) reaction mixture. Preferably, the vessel which contained theStep (1) mixture is rinsed with toluene which is then charged to theStep (3) reactor. The exothermic reaction mixture becomes reddish brownin color. A temperature rise of about 15° C. is usually observed.

A chloride-containing oxidizing agent, such as dichloromethane or silverchloride, is then charged to the reaction vessel utilized in Step (3).The resulting reaction mixture is agitated for a time appropriate,usually about two hours, for the Step (3) reaction to occur.

Solvents are removed under reduced pressure, i.e., 60-80 mm Hg, to aboutone-half of the starting volume. Hydrocarbon solvent, e.g., toluene, isadded back, Celite® filter aid is added, and the mixture is filtered.Solvents are distilled to concentrate the product.

The solid titanocene can be isolated from this mixture by methodsdependent upon the actual compound being produced. For the (CpSA)²⁻TiCl₂example shown in FIG. 1, the solid product was collected in 75-80% yieldas described in Example 6. Additional material of lower purity can beisolated upon further manipulation of the mother liquors. Alternatively,the product solution obtained after removal of the magnesium salts canbe used directly to produce other metallocenes described in Example 6.

EXEMPLIFICATION OF THE INVENTION Preparative Procedures For TitaniumTrichloride Reactant Mixtures and Resulting Metallocenes

The general procedure for the preparation of titaniumtrichloride-containing mixtures by the reaction of titaniumtetrachloride and an organometallic compound under an inert atmosphereis first described, followed by three specific examples. The reactionapparatus consisted of a 500-mL 3-neck flask equipped with a mechanicalstirrer. On one side-neck was placed a Claisen adapter with a refluxcondenser and a thermometer inserted into the reaction mixture. Thisapparatus was previously dried and then purged with nitrogen afterassembly. The solvent was added via the other side-neck of the reactionflask, which was then capped with a rubber septum. TiCl₄ (ca. 25 mL,42-44 g. 0.22-0.23 mol) was transferred from a weighed bottle to thereaction flask using a syringe. The rubber septum was replaced with adried, nitrogen-purged addition funnel. The THF and/or theorganometallic compound was transferred to the addition funnel and thenadded to the TiCl₄/solvent reaction mixture at the desired temperature.

EXAMPLE 1

A solution of n-butyllithium (BuLi) in hexanes (156 mL of a 1.60 Msolution, 0.250 mol of BuLi) was added to TiCl₄ (43.0 g, 0.227 mol) in300 mL of toluene over 30 min. The initial temperature of the reactionmixture was 10° C., the temperature increased to 40° C. during theaddition, and was then maintained at 35-40° C. using external cooling.After the addition of the BuLi, the reaction mixture was stirred at35-40° C. for 1 hour. After cooling to room temperature, the additionfunnel, condenser, and Claisen adapter were removed while maintaining aninert atmosphere of nitrogen over the TiCl₃ product mixture. Theresulting TiCl₃ containing mixture was used directly in reactions withdeprotonated metallocene ligands.

EXAMPLE 2

THF (100 mL) was added to a solution of TiCl₄ (43.4 g, 0.229 mol) in 200mL of toluene over 30 minutes at 0-15° C. Then BuLi in hexanes (156 mLof a 1.60 M solution, 0.250 mol) was added over 40 min at 5-10° C. Theresulting mixture was heated to 35-40° C. and stirred for 1 hour. Aftercooling, the resulting TiCl₃ slurry was used directly in reactions withdeprotonated ligands.

EXAMPLE 3

THF (75 mL) was added to a solution of TiCl₄ (42.0 g, 0.221 mol) in 150mL of toluene over 20 min at 0-15° C. Then a solution of butylmagnesiumchloride (BuMgCl) in THF (115 mL of a 2.10M solution, 0.242 mol ofBuMgCl) was added over 30 min. The initial temperature of the reactionmixture was 0° C.; the temperature increased to 40° C. during theaddition and was then maintained at 35-40° C. using external cooling.After the BuMgCl addition, the reaction mixture was stirred for 1 hourat 35-40° C. The resulting TiCl₃ product slurry was used directly inreactions with deprotonated ligands.

EXAMPLE 4 The Deprotonation of CpSA Ligand With i-PropylmagnesiumChloride

The reaction apparatus consisted of a 2000-mL 3-neck flask equipped witha mechanical stirrer; on one side-neck was placed a Claisen adapter witha Vigereaux column and distillation head for solvent distillation. Athermometer was inserted into the reaction flask through the Claisenadapter. The glass apparatus was previously dried and purged withnitrogen after assembly. Toluene (425 mL) and CpSA ligand (55.0 g, 0.219mol) were added to the reaction flask. The temperature of the reactionmixture was adjusted to 45-50° C. A solution of i-propylmagnesiumchloride (i-PrMgCl) in ether (205 mL of a 2.30 M solution, 0.472 mol ofi-PrMgCl) was added over 1 hour using an addition funnel. After thei-PrMgCl addition, the reaction mixture was gradually heated to 85-90°C. over 2 hours and stirred at this temperature for an additional 2hours. The (CpSA)²⁻(MgCl)₂ formed a gummy solid at this stage. Theheating is removed and the temperature of the reaction mixture cooled to60-65° C. At this temperature, THF (150 mL) was added dropwise over 15min, which dissolved the solid (CpSA)²⁻(MgCl)₂. The reaction mixture isthen cooled to room temperature. The distillation head, Vigereauxcolumn, and addition funnel are then removed from the reaction apparatuswhile maintaining an inert atmosphere of nitrogen over the productmixture. This (CpSA)²⁻(MgCl)₂ solution was then used directly in areaction with a TiCl₃ slurry prepared previously.

EXAMPLE 5 The Deprotonation of CpSA Ligand with n-Butyllithium

The reaction apparatus consisted of a 2000-mL 3-neck flask equipped witha mechanical stirrer; on one side-neck was placed a Claisen adapter witha reflux condenser and a thermometer inserted into the reaction flask.The glass apparatus was previously dried and purged with nitrogen afterassembly. Ether (300 mL) and CpSA ligand (62.9 g, 0.250 mol) were addedto the reaction flask. The reaction mixture was cooled to −20° C. Asolution of BuLi in hexanes (305 mL of a 0.170 M solution, 0.518 mol ofBuLi) was added over 1.5 hours; the temperature was maintained at −20 to−15° C. during this addition. The reaction mixture was then warmed to0-5° C. over 1.5 hours and stirred at this temperature for 3 hours. Theresulting (CpSA)²⁻Li₂ slurry, which consisted of a white solid with apale yellow supernatant, was used directly in a reaction with a TiCl₃slurry prepared as described in Examples 1 to 3.

EXAMPLE 6 The Preparation of (CpSA)²⁻TiCl₂

The TiCl₃ containing mixture from Example 1 above was transferred undernitrogen pressure via a wide-bore cannula to the (CpSA)²⁻(MgCl)₂solution from Example 4 above over 2-3 min. Toluene (100 mL) was addedto the TiCl₃ flask which contained some residual TiCl₃, and this washwas quickly transferred to the reaction flask. The initial temperatureof the reaction mixture was 22° C.; the temperature increased to 35° C.during the TiCl₃ addition. The reaction mixture was stirred for 15 minat 35° C., at which time dichloromethane (13.5 g) was added over 1 min;the temperature increased to 38° C. The resulting red-brown mixture wasstirred for 2 hours with gradual cooling to 25° C. Solvents were removedby simple distillation under reduced pressure (60-80 mm Hg) to a finalvolume of ca. 600 mL; the temperature ranged from 30 to 60° C. duringthis distillation. After cooling to 20° C. and pressurizing withnitrogen, toluene (400 mL) was added to the product mixture. Magnesiumsalts were removed from this mixture by pressure filtration undernitrogen using Celite® filter-aid. The reaction flask and filter cakewere washed with two 200-mL portions of fresh toluene. The red-brownfiltrate was concentrated by simple distillation under reduced pressureas before to a volume of 400 mL. This toluene solution is again filteredunder nitrogen pressure to remove residual magnesium salts. The filtrateis concentrated again to a volume of 200 mL by simple distillation underreduced pressure. Heptanes (400 mL) were added over 30 min with stirringat 20-25° C. A first crop of orange, crystalline (CpSA)²⁻TiCl₂ iscollected by filtration under nitrogen, washing with heptanes, to give61.1 g of product in 76% yield. A second crop was obtained byconcentration of the mother liquors to ca. 100 mL and dilution withheptanes.

Alternatively, the product solution in toluene obtained after removal ofthe magnesium salts was used directly to prepare other metallocenes. Forexample, the toluene solution of (CpSA)²⁻TiCl₂ was treated with 2equivalents of methylmagnesium chloride (THF solution) to give(CpSA)²⁻Ti(CH₃)₂ in 70-75% overall yield.

What is claimed is:
 1. In a process for producing a constrained geometrytitanocene catalyst wherein a titanium trichloride reagent is reactedwith a constrained geometry titanocene catalyst, the improvement whichcomprises: (i) utilizing as said titanium trichloride reagent a mixtureproduced by reacting titanium tetrachloride with a compound having theformula R—M, in which R is a straight or branched chain alkyl grouphaving 2 to 8 carbon atoms and M is an alkali metal, or the formulaRMgX, in which X is a halogen in substantially stoichiometric amount ina non-interfering solvent wherein a reaction mixture containing titaniumtrichloride, said solvent and a MCl or MgCl₂ is produced; and (ii)reacting said step (i) reaction mixture directly with said titanoceneligand to produce a titanocene.
 2. The process of claim 1 in which saidtitanium trichloride and said ligand are reacted at a temperature in therange of −20 to 120° C.
 3. The process of claim 1 in which said compoundRM is added to titanium tetrachloride at an initial temperature range of10-20° C., after which the reaction mixture is heated to 34-40° C. forabout one hour.
 4. The process of claim 1 in which an non-interferingsolvent is an ether.
 5. The process of claim 4 in which the ethersolvent is a cyclic ether or a polyether.
 6. In a process for producinga constrained geometry titanocene catalyst wherein a titaniumtrichloride reagent is reacted with a constrained geometry titanocenecatalyst ligand, the improvement which comprises: (i) utilizing as saidtitanium trichloride reagent a mixture produced by reacting titaniumtetrachloride with a compound having the formula R-M, in which R is astraight or branched chain alkyl group having 2 to 8 carbon atoms and Mis an alkali metal, or the formula RMgX, in which X is a halogen insubstantially stoichiometric amount in a non-interfering solvent whereinsaid non-interfering solvent is a hydrocarbon; and (ii) reacting saidstep (i) reaction mixture directly with said said constrained geometrytitanocene catalyst ligand to produce a titanocene.
 7. The claim 6process wherein said hydrocarbon solvent is a hexane, heptane, abenzene, a toluene, a xylene, or a mixture thereof.
 8. The claim 6process wherein said non-interfering solvent is dimethyl ether, diethylether or dibutyl ether.
 9. In a process for producing a titanocenewherein a titanium trichloride reagent is reacted with a titanoceneligand, the improvement which comprises: (i) utilizing as said titaniumtrichloride reactant a mixture produced by reacting titaniumtetrachloride with a compound having the formula R—M, in which R is astraight or branched chain alkyl group having 2 to 8 carbon atoms and Mis an alkali metal, or the formula RMgX, in which X is a halogen insubstantially stoichiometric amount in a non-interfering liquid mediumwherein a reaction mixture containing titanium trichloride, said solventand MCl or MgCl₂ is produced; (ii) reacting, said step (i) reactionmixture with a deprotonated titanocene ligand to produce a secondreaction mixture including said liquid medium, and a titanocenecorresponding to said titanocene ligand; and (iii) optionally isolatingsaid titanocene of step (ii) from said step (ii) second reactionmixture.
 10. In a process for producing a titanocene wherein a titaniumtrichloride reactant is reacted with titanocene ligand, the improvementwhich comprises: (i) utilizing as said titanium trichloride reactant amixture produced by reacting titanium tetrachloride with a compoundhaving the formula R—M, in which R is a straight or branched chain alkylgroup having 2 to 10 carbon atoms and M is an alkali metal, or theformula RMgX, in which X is a halogen in substantially stoichiometricamount in a non-interfering solvent wherein a reaction mixturecontaining titanium trichloride, said solvent and MCl or MgCl₂ isproduced; (ii) reacting said step (i) mixture with a deprotonatedtitanocene ligand to produce a reaction mixture including said solvent,and a titanocene corresponding to said titanocene ligand and MCl orMgCl₂; (iii) separating said MCl or MgCl₂ from said step (ii) reactionmixture; and thereafter (iv) utilizing said step (ii) reaction mixtureto prepare another titanocene.
 11. A method for producing a constrainedgeometry titanocene catalyst which comprises: (i) reacting n-butyllithium or isobutyl lithium with titanium tetrachloride in substantiallystoichiometric amount in a non-interfering hydrocarbon medium to producea first reaction mixture containing titanium trichloride and lithiumchloride; and (ii) combining said first reaction mixture with atitanocene ligand in a non-interfering medium for reaction to produce atitanocene corresponding to said ligand.
 12. The claim 11 method inwhich said titanocene corresponding to said ligand produced in step (ii)is (CpSA)²⁻TiCl₂ ([(t-butylamido)(tetramethylcyclopentadienyl)dimethylsilane]titanium dichloride).